VIBRATIONAL ANALYSIS OF THE PHENYLAZONAPHTHOL PIGMENT CA4B

Resonance Raman scattering and surface-enhanced resonance Raman scatte ring (SERRS), for the commercial phenylazonaphthol pigment Ca4B and th e structural analogue (CI 15800 in H2O and D2O and SERRS for Solvent Y ellow 14 (SY14) in H2O and D2O are presented. The greater signal-to-no ise ratio and the advantage of fluorescence quenching mean that SERRS gives more information than resonance scattering. The spectra confirm that CI 15800 is closely related in structure to Ca4B, indicating that the calcium-complexing site in Ca4B is mainly associated with the ket o and carboxyl groups, with the sulphonic acid group playing a minor p art. A semiempirical calculation using the PM3 Hamiltonian is used to assign scattering from CI 15808 and Ca4B, The most intense Raman scatt ering, due to in-plane modes with the largest displacements on the phe nyl and naphthol rings, is correctly assigned. Further, the calculatio n predicts changes due to deuterium exchange of the hydrogen associate d with the hydrate group which are borne out by experiment. Hence Rama n scattering provides a good in situ probe of the hydrogen-bonded netw ork essential to the properties of these compounds. (C) 1998 John Wile y & Sons, Ltd.